1. Field of the Invention
The present invention relates to a damping device for a moonpool, and more particularly, to a damping apparatus for a moonpool, which has a simple driving mechanism.
2. Description of the Related Art
With the development of offshore drilling techniques, drill ships equipped with drilling equipment suitable for development of small marginal fields or deep-sea oil fields have been developed.
In a conventional offshore drilling, rig ships or fixed type platforms have been mainly used, which can be moved only by tugboats and are anchored at a position on the sea using a mooring gear to conduct an oil drilling operation. In recent years, however, so-called drill ships have been developed and used for offshore drilling. The drill ships are provided with advanced drilling equipments and have structures similar to typical ships such that they can make a voyage using their own power. Since drill ships have to frequently move in order for development of small marginal fields, they are constructed to make a voyage using their own power, without assistance of tugboats.
Meanwhile, a moonpool through which a variety of equipments for a drilling operation pass is installed in an offshore platform such as a drill ship or a drill rig. The moonpool has a hollow parallelepiped or cylindrical structure through which a variety of equipments are vertically moved between an upper deck and a bottom of an offshore platform.
As the size of an offshore platform increases, a moonpool also becomes larger. Accordingly, in the case of a parallelepiped moonpool, a large moonpool with a size of 12-13 m (a length in a width direction of an offshore platform)×14-25 m (a length in a front and rear direction of an offshore platform) has been used. Such a moonpool is indispensable in terms of the purpose of a drill ship, but is very disadvantageous in terms of anchoring of the ship, voyage stability and voyage performance of the ship.
In particular, a sloshing phenomenon is induced by a relative movement between seawater flowing into the moonpool and seawater outside the hull of the ship. The sloshing phenomenon may cause an increase in voyage resistance, a decrease in voyage speed, an increase in power consumption and fuel consumption, and a damage of a hull.
In addition, an overflowing phenomenon is induced by a fluid movement inside the moonpool. The overflowing phenomenon may serve as a factor that deteriorates a worker's safety and work efficiency.
Accordingly, a damping plate which opens and closes the moonpool is installed in order to minimize the movement resistance of the hull and effectively prevent the overflowing phenomenon caused by high waves. One or two damping plates are hinged to a sidewall of the moonpool to open and close the moonpool. The opening and closing operation of the damping plates is handled by a deck crane disposed at the deck of the hull.
In the case of an arctic drill ship, however, since a derrick disposed above a moonpool is configured with an enclosed structure, a deck crane of a hull cannot approach the inside of the moonpool. Therefore, a separate driving mechanism (e.g., a winch or a cylinder) for driving a damping plate is required within the moonpool and the derrick disposed above the moonpool. Consequently, installation cost increases and interference with other articles is caused, making an installation layout cumbersome.